1. Field of the Invention
The present invention relates to a rotary swivel equipped with a dynamometric measuring unit and, more especially to such a rotary swivel intended to drive a drill pipe in rotation.
2. Description of the Prior Art
There are two types of devices which can be used on a drilling mast for driving a string of pipe in rotation. The first, and the more traditional, is the rotary turn-table which is mounted on the floor of the drilling mast and comprises a square or hexagonal opening intended to receive a drive rod of complementary cross-section. The turn-table is set in rotation and thus causes the rotation of the string of pipe
The other type of device is the motorised rotary swivel, where an electric or hydraulic motor, mounted adjacent to the movable pulley block, is linked directly to the upper end of the string of pipe. The motor is mounted on a carriage which slides on rails arranged vertically on the mast thus permitting the movement of the carriage whilst absorbing the torque generated during drilling.
On the other hand, there are dynamometric measuring units which are intended to be mounted on the string of pipe in order to be able to measure the forces and sense the various vibrations of the said string of pipe which are generated during drilling and which can be characteristic either of the behaviour of the string of pipe, or of the state of wear of the tool, or even of the type of rock being destroyed.
Patent Application FR 89 08649 which was filed on 28 Jun. 1989 in the name of the applicant describes such a dynamometric measuring unit for drill pipe in which a series of sensors is mounted on a drill-rod element of reduced length, more ordinarily called "sub". This device is mounted on the upper end of the string of pipe below the automatic wrench which is arranged at the output of the motor.
Despite these advantages, the positioning of the dynamometric measuring unit below the dynamometric wrench is a source of difficulties because, during certain manoeuvres, for example the withdrawal of only some elements of the string of pipe whilst maintaining the circulation of mud, it is necessary to withdraw the measuring unit beforehand. Extra time, resulting from this withdrawal and reassembly of the measuring unit, is thus added to the manoeuvre.